Class

We define the classes principle and example in the style sheet or wherever as follows:

.principle{background-color: rgb(255,255,0); color: rgb(0,0,255)}

.example{background-color: rgb(255,255,0); color: rgb(0,0,255)}

Note the dot before principle and example when they are defined. We can
use these classes in almost any element (or selector) we choose. However, we could have
defined them, for example, as follows using the paragraph selector:

p.principle {statements}

And this would apply only to paragraphs. We could then define similar class selectors
for other elements having the same name, but different effects.